Field of the Disclosure
This disclosure relates generally to orthopedic devices, and more specifically, to a bone fixation system, apparatus, and method with anti-back out feature.
Background of the Disclosure
For various bone fractures, the use of orthopedic plates is a well-known technique to stabilize the bone as needed for proper healing. Generally, a rigid, often metal plate is placed on the outer surface of the bone across the fracture, and orthopedic screws extend through the plate into the bone on either side of the fracture. The plate offers support and stability to the bone during the healing period. Typically, the orthopedic screws have threads along a shaft, which are adapted to engage bone. The head portion of the screw is commonly a standard screw head that provides a compressive force as the screw is threaded into the bone, thereby compressing the orthopedic plate against the bone.
It may also be necessary to secure and stabilize the cervical vertebrae during spinal fusion surgeries. Stabilization of the cervical vertebrae facilitates an appropriate healing or a preferred result. In such situations, an orthopedic plate may be mounted on one or more vertebrae during the surgery using orthopedic screws. The plates are firmly secured to the spinal column so that the plates are not broken when stressed. Typically, screws are used to mount the cervical plate to the one or more vertebrae.
The term “micromotion” refers to microscopic relative displacements of a loaded intraosseously implanted orthopedic hardware component with respect to the bone surrounding it. Micromotion between the bone and the portion of the orthopedic screws within the bone or vertebrae can cause loosening of one or more orthopedic screws, often called back out. When screw back out occurs, loosening of the entire assembly occurs, thereby diminishing the stability of the set fracture or spinal fusion.
To address screw back out, some orthopedic systems have used screws with threaded heads. In such systems, the head of the screw threadably engages in threads in the orthopedic plate to lock the screws relative to the plate. These systems, however, do not provide the necessary control of compression between the plate and bone because the screw is locked relative to the plate. Accordingly, this type of system provides sub-optimal stability for attachment of orthopedic plates to bone(s). In addition, the threaded engagement between the screw and plate can loosen over time.
Other systems use secondary discrete hardware to lock a bone screw to the plate. For example, some systems use a set screw that sets against the head of the orthopedic screw to prevent back out of the screw. In another system, a washer and screw assembly is used in combination to provide compression against the head of the orthopedic screw and prevent back out. Such systems increase the number of individual hardware pieces for a given application, increasing not only the complexity of installing an orthopedic plate, but also the chances of an object being lost in the surgical wound.
The use of the same reference symbols in different drawings indicates similar or identical items. Items in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.